1. Field of the Invention
The present invention relates generally to intravascular radiation therapy. More specifically, the present invention relates to radiation therapy for inhibition of vascular restenosis using an intravascular radioactive implantable device and a radiosensitizer agent.
2. Description of Related Art
In a typical balloon PTCA procedure, a catheter is inserted into the cardiovascular system via a femoral artery under local anesthesia. A pre-shaped guiding catheter is positioned in the coronary artery, and a dilatation catheter having a distensible balloon portion is advanced through the guiding catheter into the branches of the coronary artery until the balloon portion traverses or crosses a stenotic lesion. The balloon portion is then inflated with an inflation medium to compress the stenotic lesion in a direction generally perpendicular to the wall of the artery, thus dilating the lumen of the artery.
Patients treated by PTCA procedures, however, suffer from an incidence of restenosis i.e., at or near the original site of the stenosis in which the coronary vessel collapses or becomes obstructed by extensive tissue growth intimal hyperplasia. When restenosis occurs, a second angioplasty procedure or even bypass surgery may be required, depending upon the degree of restenosis.
Clinical studies have indicated that anti-proliferative drug therapy or intravascular radiation after balloon angioplasty or an atherectomy procedure can prevent or reduce the rate of restenosis caused by intimal hyperplasia. In order to reduce or prevent restenosis, anti-proliferative agents or intravascular radiotherapy or radiation therapy is generally given at high toxicity or very high doses. For many patients, however, receiving high doses of radiation in a short amount of time could have long-term negative consequences. In addition, treating patients with high dose radiotherapy e.g., external radiation beam or brachytherapy may only be performed in specially built facilities and requires strict adherence to numerous radiation safety regulations, ultimately adding to the cost of the procedure.
To overcome the disadvantages associated with high-dose radiotherapy procedures, medical practitioners have increasingly relied on low-dose intravascular radiation therapy i.e., radiotherapy for treatment of restenosis. One approach of performing low-dose intravascular radiotherapy involves inserting a flexible catheter into the cardiovascular system of a patient and then advancing the catheter to the region of the vessel that has been subjected to the angioplasty procedure. A radiation source or a treatment catheter having a radiation source inside is then advanced through the flexible catheter so that the radiation source reaches the stenosed vascular site and can deliver an effective dose of radiation. After the radiation treatment is completed, the catheter and radiation source are removed.
Another approach of performing intravascular radiotherapy to prevent or reduce the rate of restenosis involves the use of an implantable radioactive device, such as a radioactive stent, with either beta-emitting or gamma-emitting radioisotopes. Intravascular implantation of a radioactive stent generally involves advancing the stent on a balloon catheter or a similar device to the designated vessel site and deploying the stent by inflating the balloon which then expands the stent radially against the wall of the vessel. Once the stent is properly positioned and secured in place at the vessel site, the balloon is deflated and the catheter is removed from the patient.
The use of implantable radioactive stents, however, is not without some disadvantages. Preliminary clinical studies indicate that although a radioactive stent will eliminate the proliferation of smooth muscle cells e.g., following a PTCA or stent procedure inside the vessel area of the stent, the use of implantable radioactive stents may increase the restenosis rate in the area of the vessel immediately beyond the longitudinal ends of the stent e.g., xe2x80x9cstent edge effectsxe2x80x9d. The smooth muscle cell growth immediately beyond the implanted radioactive stent tends to resemble a shape not unlike the ends of a candy wrapper. Hence, some in the medical community generally apply the term xe2x80x9ccandy wrapperxe2x80x9d to this phenomenon.
Although the precise cause of the xe2x80x9cstent edge effectsxe2x80x9d is currently unknown, some in the medical community have suggested that these effects may be caused by the use of a radioactive stent having a length smaller that the actual length of the vessel site that was treated during angioplasty coupled with the failure or inability to properly treat the entire vessel lesion site with sufficient amounts of radiation.
Some techniques for minimizing thrombus formation, inflammation and restenosis of the vessel have been focused on improving the design of the radioactive stent and/or its delivering device e.g., catheter balloon to permit for a smoother and more precise implantation of the stent at the vessel treatment site. Other techniques rely on coating the surface of the radioactive stent with various types of drugs or substances to inhibit the proliferation of smooth muscle cells. Still yet other techniques use xe2x80x9chot endsxe2x80x9d and xe2x80x9cunevenxe2x80x9d dose loading along the stent when trying to eliminate the xe2x80x9ccandy wrapperxe2x80x9d effects and/or to increase the effective dose rate range for radioactive implantable stents. None of the these techniques, however, are effective in preventing or minimizing the xe2x80x9cstent edge effectsxe2x80x9d or xe2x80x9ccandy wrapperxe2x80x9d effects associated with the use of radioactive stents.
Given the significant clinical benefits associated with the use of implantable radioactive stents to prevent or reduce vascular restenosis, it is useful to develop a method that will eliminate one of the possible mechanisms causing the xe2x80x9cstent edge effectsxe2x80x9d or xe2x80x9ccandy wrapperxe2x80x9d effects: the failure or inability to properly treat the entire vessel lesion site with sufficient amounts of radiation. To this end, it is advantageous to develop a method that will enable the effective dose range of the radiation to extend as far as possible outside the radioactive stent and thus allow the injured vessel site beyond the length of the stent to be properly treated. It is also helpful that this method be made as minimally invasive as possible and without any significant adverse health effects to the patient. Furthermore, it is useful that this method be simple to implement and be as safe as possible to patients and health care professionals.
A method for inhibiting vascular restenosis is described. In one embodiment, the method includes implanting a medical device at a blood vessel site that has undergone a procedure to open a stenosed region within a blood vessel. The medical device contains a radioisotope to emit a radioactivity to a tissue mass at the blood vessel site. The method further includes delivering a radiosensitizer agent to the tissue mass at the blood vessel site. The radiosensitizer agent increases a therapeutic response of the tissue mass to the radioactivity emitted by the radioisotope.